Fluid energy converter

ABSTRACT

A fluid energy converter, such as windmill or a wind turbine, includes a rotor having a front rotatable hub and a back rotatable hub. In some embodiments, a plurality of blades extends from the front hub to the back hub. A suitable blade includes a front section, a tip, and a back section. In one embodiment, the chord of the tip cross section is at an angle relative to the tangent of the rotor radius. The tip chord can be perpendicular to the direction of movement of the fluid. In some cases, the profile of a blade front section, from its root to the tip, forms a concave curve. In one case, the profile of the blade tip, from a junction root to the tip, forms a convex curve. A front section, an apex, and a back section of a blade form a generally parabolic shape.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 61/171,033, filed Apr. 20, 2009, the disclosure of which is hereby incorporated by reference in its entirety. This application also incorporates herein by reference in its entirety U.S. patent applications Ser. No. 11/506,762, filed on Aug. 18, 2006 and 11/746,482, filed on May 9, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates generally to fluid energy converters, and more particularly the invention relates to windmills and wind turbines.

2. Description of the Related Art

Fluid energy converters typically use blades, propellers, or impellers to convert kinetic energy of a moving fluid into mechanical energy, or to convert mechanical energy into kinetic energy of a moving fluid stream. For example, windmills and waterwheels convert kinetic energy from the wind or water into rotating mechanical energy, and wind turbines and water turbines further employ a generator to convert the rotating mechanical energy into electrical energy. In the reverse process, fans, propellers, compressors, and pumps can be configured to impart kinetic energy, from rotating mechanical energy, to a fluid.

Energy conversion, from kinetic to mechanical, for gases can be inefficient, especially with windmills and wind turbines. It is generally accepted that the highest efficiency possible for devices converting kinetic energy from the wind is about 59.3%. However, this number neglects losses which occur from drag and turbulence, for example. Some utility class three blade wind turbines can achieve peak efficiencies of over 50%, while windmills are significantly lower. Therefore, there exists a need for a more efficient fluid energy converter for wind applications.

While some fluid energy converters for use with liquid fluids can achieve high efficiencies, these machines are expensive. For example, although Francis water turbines can achieve efficiencies of over 90%, they are extremely expensive. Applications exist where cost is a more important factor than efficiency maximization, and thus there exists a need for a lower cost fluid energy converter for liquid flows that still maintains a desirable efficiency.

Summary of Certain Inventive Embodiments of the Invention

The systems and methods illustrated and described herein have several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope as expressed by the description that follows, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of the Preferred Embodiments” one will understand how the features of the system and methods provide several advantages over traditional systems and methods.

In one aspect, the invention relates to a rotor for a fluid energy converter. The rotor has a longitudinal axis, a front rotatable hub coaxial with the longitudinal axis. In one embodiment, the rotor has a back rotatable hub coaxial with the longitudinal axis. The rotor has a number of blades, each blade comprising a front section, a tip, and a back section. The blades are arranged angularly about the longitudinal axis. Each blade is attached at a front root attachment to the front hub and attached at a back root attachment end to the back hub. The front section comprises a pitch higher than a pitch of the back section.

In another aspect, the invention concerns a rotor for a fluid energy converter. The rotor has a longitudinal axis, a front rotatable hub coaxial with the longitudinal axis, and a back rotatable hub coaxial with the longitudinal axis. In one embodiment, the rotor has at least nine blades. Each blade is attached at a front section to the front hub and attached at a back section to the back hub. The blades are positioned radially around the longitudinal axis. Each of at least some of the blades comprises a front section, a tip, and a back section. The front section, tip, and back section use fluid foils. An angle between the tip and the chord is between 4 and −15 degrees.

In yet another aspect, the invention relates to a fluid energy converter having a longitudinal axis. In one embodiment, the fluid energy converter has a rotatable rotor coaxial about the longitudinal axis. The rotatable rotor includes a number of blades. Each blade has of a front section, a tip, and a back section. The tip chord produces tangential lift.

These and other improvements will become apparent to those skilled in the art as they read the following detailed description and view the enclosed figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a perspective view of a fluid energy converter.

FIG. 2 is a partial section view of the fluid energy converter of FIG. 1.

FIG. 3 is another partial section view of the fluid energy converter of FIG. 1.

FIG. 4A is a perspective view of a blade that can be used with the fluid energy converter of FIG. 1.

FIG. 4B is another perspective view of a blade that can be used with the fluid energy converter of FIG. 1.

FIG. 4C is a top view of a blade that can be used with the fluid energy converter of FIG. 1.

FIG. 5A is a perspective view of a front section profile of the blade of the fluid energy converter of FIG. 1.

FIG. 5B is a perspective view of a tip profile of the blade of the fluid energy converter of FIG. 1.

FIG. 5C is a perspective view of the back section profile of the blade of the fluid energy converter of FIG. 1.

FIG. 6 is a schematic of certain fluid dynamics believed to be associated with the fluid energy converter of FIG. 1.

FIG. 7 is a schematic cross sectional top view of the profile of the blade of the fluid energy converter of FIG. 1.

FIG. 8 is a schematic cross sectional front view of the profile of the blade of the fluid energy converter of FIG. 1.

FIG. 9 is a back view of a rotor of the fluid energy converter of FIG. 1.

FIG. 10 is a perspective view of another blade that can be used with the fluid energy converter of FIG. 1.

FIG. 11 is a plan view of the blade of FIG. 10.

FIG. 12 is a cross-sectional view A-A of the blade of FIG. 11.

FIG. 13 is a cross-sectional view B-B of the blade of FIG. 11.

FIG. 14 is a cross-sectional view C-C of the blade of FIG. 11.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

Embodiments of the invention will now be described with reference to the accompanying figures, wherein like numerals refer to like elements throughout. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner simply because it is being utilized in conjunction with a detailed description of certain specific embodiments of the invention. Furthermore, embodiments of the invention may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the inventions herein described.

Referring now to FIG. 1, one embodiment of a fluid energy converter 100 is shown. The fluid energy converter 100 includes a rotor 1, a tail 60, and a tower 70. The rotor 1 can have a plurality of blades 10 arranged about a longitudinal axis 8. In one embodiment, the rotor 1 has at least nine blades 10. In some embodiments, the rotor 1 has eighteen or more blades 10. The blades 10 can be generally curving structures with one or more fluid foils formed into their surfaces. Depending on the size and the desired strength-to-weight ratio, the blades 10 can be produced from materials such as sheet metal, composites (including carbon fiber, fiberglass and polyester resin), plastic, or any other suitable material. The fluid energy converter 100 is substantially similar to the fluid energy converters described in U.S. patent application Ser. No. 11/746,482, which is hereby incorporated herein by reference in its entirety.

For example, in a first aspect, a fluid turbine can have a rotatable rotor and a stand or tower. The rotor includes a longitudinal axis, a plurality of rotatable blades concentric with the longitudinal axis, a rotatable front hub concentric with the longitudinal axis, a nacelle concentric with the longitudinal axis, a rotatable back hub concentric with the longitudinal axis, and a shaft concentric with the longitudinal axis. In one embodiment, each blade incorporates a front section, a tip, and a back section.

For each blade, the root of the front section attaches to the front hub and the root of the back section attaches to the back hub. In some embodiments, the front hub and the back hub rotate over the shaft on bearings to minimize friction. The nacelle can be rigidly attached to the shaft and can have multiple helical vanes on its outer surface. The shaft can be a rigid rod or a hollow tube and attaches to the tower supporting the rotor. In one embodiment, the nacelle houses a drivetrain, which can include a speed increaser and a generator to produce electricity. In some embodiments, a tail is positioned behind and attached to the rotor, which tail is directed by the fluid stream to point the rotor into the fluid stream. The tail can have both vertical plane and horizontal plane components, which serve to position the rotor both in pitch and yaw.

In some embodiments, areas of high and low pressure are created when some fluids pass through the rotor. The fluid contacts the root of the front section of the blades as it approaches the rotor and is projected radially away from the longitudinal axis and compressed against the tip and the outer portion of the front and back sections of the blades, creating an area of high pressure relative to the surrounding fluid pressure. An area of low pressure forms near and around the longitudinal axis, and consequently, draws the fluid into the rotor. In this manner, the area of low pressure accelerates the fluid across and through the rotor. Additionally, fluid tangent to the fluid entering the rotor is directed against the outside surface of the tip and the outer portion of the front and back sections of the blades, thereby creating an area of high pressure on both the inside and outside surfaces of the tip and outer portion of the front and back sections of the blades.

In some conditions the rotor can be pitched (that is, oriented up or down in a vertical plane) and/or yawed (that is, rotated from side to side on a horizontal plane) to take advantage of beneficial effects which increase power production. The nacelle can incorporate helical vanes which direct the fluid to rotate in the same direction as the rotation of the rotor, creating a vortex and increasing power production. In another aspect, the blade tips are folded over, to increase their surface area and power producing capability.

In some embodiments, the fluid energy converter is configured so that the pitch of the front section of the blades is greater than the pitch of the back section. In this manner, the swirl behind the front section approaches the back section at an appropriate angle for power extraction. In some embodiments, the nacelle can be adapted to redirect the fluid in a beneficial direction, in which case the pitch of the back section of the blades can be greater. In some embodiments the back section of the blades are designed to direct the fluid radially away from the longitudinal axis as the fluid exits the back of the rotor. This increases the low pressure near the longitudinal axis and directly behind the rotor, increasing fluid draw into the rotor. In other embodiments the back section of the blades are configured to straighten the fluid exiting the rotor and reentering the fluid stream. This minimizes turbulence created from surrounding fluid mixing with fluid that has passed through or adjacent to the rotor. In some embodiments, the nacelle is moved forward toward the front of the rotor, to minimize the time the swirl rotates in a power reducing direction. In still other embodiments, the helical vanes of the nacelle, which direct or redirect fluid, are not used.

In still another aspect, the tail can be offset from the longitudinal axis to set the optimal pitch and yaw relative to the fluid stream. Thus, the tail axis need not be parallel with the longitudinal axis. In some embodiments, changing fluid velocity increases or decreases pressure on the tail, causing changes in pitch and yaw with varying fluid speeds.

In still another embodiment, the blades of the rotor are designed to flex so that the pitch of the blades will vary with changes in fluid velocity. In one aspect, the power train is attached to the back hub, and the front hub of the rotor is configured to spin freely. In such embodiments, the pitch of the blades can be arranged to change as pressure applied to the blades by the fluid varies with changes in fluid velocity.

Referring now to FIGS. 1, 2, and 3, one embodiment of a fluid energy converter 100 is shown. The fluid energy converter 100 includes a rotor 1, a power train 80, a tail 60, and a tower 70. In one embodiment, the rotor 1 can have a plurality of blades 1, a front hub 34, a back hub 44, a nacelle 50, and a shaft 28. In some embodiments, the blades 10 can be generally curving structures with one or more fluid foils formed into their surfaces. Depending on the size and the desired strength-to-weight ratio, the blades 10 can be produced from materials such as sheet metal, composites (including carbon fiber, fiberglass and polyester resin), plastic, or any other suitable material.

In some embodiments, the length-to-diameter ratio of the rotor 1 is about 0.8:1, although this ratio can vary according to the application, and can range from about 1:10 to about 10:1. In embodiments where the fluid energy converter 100 produces energy, the blades 10 are preferably configured to capture kinetic energy of a moving fluid, such as air or water, and convert the captured kinetic energy into rotating mechanical energy. In embodiments where the fluid energy converter 100 moves a fluid, such as in a compressor or pump, the blades 10 are preferably adapted to direct the fluid in a desired direction. In some embodiments, the blades 10 can be configured to compress and/or accelerate the movement of the fluid. As used here, when referring to the interaction between a fluid or fluid stream and the blades 10 (or rotor 1), the term “capture” refers to a resistance provided by the blades 10 or rotor 1 that, among other things, increases the volume of fluid entering the rotor 1 and/or increases the transfer of kinetic energy from the fluid to the rotor 1.

Referring now to FIGS. 1-5C, one embodiment of the blades 10 is described. The blades 10 are generally long, slender, curving shapes that are attached at a front end and a back end, respectively, to the front hub 34 and the back hub 44. The blades 10 can be curved to maximize energy production in a fluid energy converter 100 that converts the kinetic energy in a fluid to rotating mechanical energy, or to optimize directing fluid when the fluid energy converter 100 converts rotating mechanical energy to kinetic energy in a fluid. In some embodiments, the front section 12 of each blade 10 has a front curve 17, where an averaged center (not shown) of the front curve 17 is positioned toward the front of the blade 10 and radially away from the longitudinal axis 8. In some embodiments, the front curve 17 is not a single radius and, rather, is formed from multiple radii. In one embodiment, a convex side of the front curve 17 faces toward the longitudinal axis 8 and the back of the rotor 1, while the concave side of the front curve 17 faces toward the averaged center. In some embodiments, the pitch of the front section 12 varies from the front root attachment 13 to the front transition 16 near the tip 18 to account for changes in the angular velocity of the blade 10. In some embodiments, the pitch of the front transition 16 can be 30 degrees, while the pitch of the front root attachment 13 can be 50 degrees. In other embodiments, the pitch and the twist of the front section 12 will vary according to the application. In some embodiments, the back section 22 can include a back transition 26 with a pitch of 20 degrees, while the pitch of the back root attachment 23 can be 40 degrees. In some embodiments the twist, or change in pitch is linear from the front transition 16 to the front root attachment 13, and from the back transition 26 to the back root attachment 23. In other embodiments, the twist is non-linear and increases toward the front root attachment 13 and the back root attachment 23. In applications with high angular velocities, the pitch of the blades 10 will generally be less, can approach zero degrees, and in some cases can be negative. For example, in a wind turbine with a high angular velocity, the pitch of the front transition 16 can be zero degrees and the pitch of the back transition 26 can be negative 10 degrees. In embodiments with low angular velocities and/or different fluids, the pitch of the blades 10 can be greater than 60 degrees. In some embodiments, the front section 12 and the back section 22 the same pitch, while in other applications the pitch of the back section 22 is greater than the pitch of the front section 12. In some embodiments, such as wind turbines, the pitch of the back section 22 can be 10 degrees less than the pitch of the front section 12.

Still referring to FIGS. 1-5C, each blade 10 is composed of a front root attachment 13, a front section 12, a tip 18, a back section 22, and a back root attachment 23. The front root attachment 13 is used to attach each blade 10 to the front hub 34 and includes one or more front tabs 14. In some embodiments, the front tabs 14 can have one or more front holes 15 through which a standard fastener (not shown) is inserted to attach the blade 10 to the front hub 34. In some embodiments, two front tabs 14 are used, one to attach the blade 10 to the front of the front hub 34 and the other to attach the blade 10 to the back of the front hub 34. In some embodiments, the front hub 34 and the back hub 44 are similar, although in some applications the nacelle 50 is located at the front of the rotor 1, thereby necessitating a different configuration for the front hub 34. In some embodiments, the back root attachment 23 uses the same method to attach the back section 22 to the back hub 44. Two back tabs 24, each having one or more back holes 25 are configured to provide an attachment to the back hub 44.

The front hub 34 and the back hub 44 are generally cylindrical tubes, each having a bore in the center to allow the insertion of a front bearing 38 in the front hub 34 and a back bearing 48 in the back hub 44. The front hub 34 and the back hubs 44 are rigid, load carrying components, and depending on the application can be made from metal, such as aluminum and steel, plastic (including plastics which can be molded), composite material (such as carbon fiber), or any other suitable material. The front hub 34 and the back hub 44 can have a plurality of front and back slots 30, 40, which can be cut into the hubs 34, 44, at the same angle as the front root attachment 13 and the back root attachment 23. The root attachments 13, 23, can be inserted into the slots 30, 40, and secured with standard fasteners which are threaded into the hub holes 32, 42. In some embodiments the hub holes 32, 42 are not threaded but provide clearance for bolts (not shown) which extend from the first of the front and back tabs 14, 24, through the hub holes 32, 42, and finally through the second front and back tabs 14, 24. In some embodiments, nuts and lock washers (not shown) are used to tighten and secure the bolts.

Still referring to FIGS. 1-5C, the front transition 16 denotes the transition from the front section 12 to the tip 18. The twist of the pitch continues to the outermost portion of the tip 18 where the pitch in some embodiments is zero degrees. In some embodiments, the chord at the outermost portion (the portion defining the outside diameter of the rotor 1) of the tip 18 is not tangent to a circle defining the outside diameter of the rotor 1, but is offset at an angle to this tangent. As used here, the term “tangential pitch” refers to the chord angle relative to the tangent of the circle defined by the outermost portion of the tip 18. The tangential pitch produces lift on a plane that is 90 degrees to the plane of the lift produced by the pitch. A tangential pitch with a negative angle denotes a chord with a profile that has a leading edge radially inside of the circle and a trailing edge outside of the circle. In some embodiments, the tip 18 has a tangential pitch of −6 degrees, which denotes a chord that points slightly toward the center of the rotor 1. This negative angle creates lift in a direction that is both radially out from the center and tangentially in the direction of rotation. The tangential component of the lift pulls the rotor 1 in the direction of rotation, adding power to the rotor 1 when the fluid energy converter 100 is configured to convert kinetic energy in a fluid to rotating mechanical energy.

Still referring to FIGS. 1-5C, the fluid foils of the blades 10 are described. In some embodiments the foils of the front section 12, tip 18, and back section 22, can be different to account for differences in angular velocity from the root attachments 13, 23, to the tip 18, and also to augment power extraction by the fluid energy converter 100 in important areas, such as the tip 18. In some embodiments, a different foil can be used at the root attachments 13, 23, than at the front and back transitions 16, 26. In some embodiments, the front section 12 near the front root attachment 13 uses a flat, plate style foil 170 with rounded edges like the profile shown in FIG. 5B. At the front transition 16, the tip 18, and the back transition 26, the foil can change to a typical fluid foil 172 like that shown in FIG. 5A to account for the increase in angular velocity. Near the back root attachment 23, the fluid foil can change again to a curved foil 174 shown in FIG. 5C.

The profiles of the fluid foils 170, 172, 174 can vary depending on the angular velocity of the fluid energy converter 100, the fluid, the size, and the application. To minimize manufacturing costs, in some embodiments the fluid energy converter 100 uses the flat foil 170 over the entire length of the blade 10. In other applications, such as large wind turbines, the fluid energy converter 100 uses the fluid foil 172 over the entire length of the blade 10. In other applications involving wind turbines, the fluid energy converter 100 can use two, three, four, or more airfoils over the length of the blade 10 to account for changes in angular velocity at different areas of the blade 10. The different functions that the front section 12 and the back section 22 perform may call for different configurations of the foils 170, 172, 174. For many wind turbines, SG 6040, NACA 4412 or NACA 4415, for example, are acceptable airfoils although many different blades can be used. SD 2030 is a good choice for small wind turbines.

Still referring to FIGS. 1-5C, in some embodiments, the chord length of the blades 10 is about 6% of the diameter of the rotor 1. The optimal chord length will vary with changes in the Reynolds number, diameter of the rotor 1, velocity of the fluid, type of fluid, angular velocity, and whether the fluid energy converter 100 converts kinetic energy to rotational energy or, conversely, uses mechanical rotational energy to impart kinetic energy to a fluid. In some embodiments, the chord length will be shorter on the back section 22 than the front section 12, while in other embodiments the chord length will be longer on the back section 22 than the front section 12. In some embodiments, the chord length of the front section 12 and the back section 22 decreases in length, or tapers 10 degrees, from the hubs 34, 44 to the tip 18. In other embodiments, the chord length is longer at the hubs 34, 44 and follows a non-linear taper toward the tip 18. Generally, when a non-linear taper is used the chord length increases gradually moving from the tip 18 toward the middle of the front section 12 and back section 22, and increases rapidly from the middle of the sections 12, 22 to the hubs 34, 44, respectively.

In some embodiments, the fluid energy converter 100 suffers little to no tip loss because the tips 18 have a tangential pitch which not only produces power but also prevents fluid from escaping around the tip 18. Some embodiments of the rotor 1 take advantage of this phenomenon by utilizing a reverse taper where the chord length is longest at the tips 18 and decreases toward the hubs 34, 44, respectively. Depending on the application, the front section 12 and the back section 22 may not have the same taper, and the back section 22 can have a taper while the front section 12 has a reverse taper. In embodiments where the front and back sections 12, 22 taper in the same direction, the optimal angle of the tapers can be different. In still other embodiments, neither the front section 12 nor the back section 22 tapers the chord length. This can be for manufacturing reasons, such as stresses on the blades 10, rather than aerodynamic or hydrodynamic efficiency. Cost can also be a factor, because in some applications it is simpler to manufacture the blades 10 without tapering the chord length.

Still referring to FIGS. 1, 2, and 3, in some embodiments, such as a wind turbine or windmill, the fluid energy converter 100 includes a tail 60 configured to keep the rotor 1 pointed into the wind during changes in wind direction. In some embodiments, the tail 60 has four tail vanes 62, while in other embodiments 1, 2, 3, 4, 5, or more tail vanes 62 can be used. A tail shaft 64, generally a cylindrical rod, connects the tail 60 to the tail body 66. Preferably, a material with a high strength to weight ratio is used to construct the tail 60 components; such a material can be aluminum, titanium, carbon fiber, fiberglass and polyester or epoxy resin, or plastic. In some embodiments the tail vanes 62, tail shaft 64, and tail body 66 are cast, injection molded, rapid prototyped, or machined as one part.

In some embodiments, the tail body 66 has at least two cavities, including one to accept insertion of the shaft 28. The shaft 28 can be rigidly attached to the tail body 66 by using fasteners, welding, adhesive, an interference fit, or any other suitable method. The tail body 66 also has hinge pin holes 68 which have an axis that is perpendicular to the shaft 28, and lie on a plane parallel with the surface upon which the tower base 72 rests. The hinge pin holes 68 allow insertion of hinge pins (not shown) which are pressed into the tail body 66 with an interference fit. A second cavity in the tail body 66 accepts insertion of a hinge 67, which can be an interface between the tail body 66 and the tower 70; the hinge 67 allows the rotor 1 to be pitched and yawed.

The hinge 67 can be a strong, durable component that in some embodiments is made from steel or aluminum. In some embodiments, where the fluid energy converter 100 is small and/or the loads are light, the hinge 67 can be made from molded plastic, such as glass filled nylon, or a composite. The hinge 67 includes a counterbore which has an axis that is perpendicular to the axis of the shaft 28 and has an inside diameter slightly larger than the diameter of the tower 70 at its uppermost portion. A tower bearing 78, which in some embodiments is a needle thrust bearing, has an outside diameter that is approximately the same as the diameter of the uppermost portion of the tower 70, and is positioned inside the counter bore of the hinge 67 between the tower 70 and the hinge 67. The tower bearing 78 provides low friction yawing of the rotor 1. In one embodiment, the hinge 67 has two blind holes near its uppermost portion to allow insertion of the hinge pins 65 which are inserted through the hinge pin holes 68. The hinge pin holes 68 are preferably of a diameter slightly larger than the hinge pins 65 to allow the hinge pins 65 to rotate freely. In some embodiments, the tail 60 is not used and, instead, a commonly known yaw drive is used to control the yaw of the rotor 1 and maintain a desired orientation of the rotor 1 with respect to a fluid stream.

Theoretical descriptions of various modes of power extraction by the fluid energy converter 100 follow. Actual performance of any given embodiment of the energy converter 100 and/or rotor 1 is governed by a multiplicity of factors; hence, the following descriptions of operational principles are to be understood as generalized, theoretical, and/or not limiting upon the inventive embodiments of the devices and their methods of use described herein, unless otherwise specifically stated.

Referring now to FIGS. 1 and 6, a pressure differential effect through the rotor 1 is described. FIG. 6 shows a schematic of the rotor 1 in a flowing fluid 112, where the direction of the flow of fluid 112 is denoted by arrows. As the fluid 112 contacts the front section 12 of the blades 10 when the rotor 1 is rotating, the fluid 112 is directed radially away from the center of the rotor 1. The effect of this phenomenon is that an interior high pressure area 111 forms on the inside surfaces of the blade tips 18, and an interior low pressure area 100 forms in the center of the rotor 1. The interior low pressure area 110 causes the fluid 112 at the front of the rotor 1 to accelerate. When the fluid 112 is air, the available power increases by the cube of the increase in wind velocity.

By way of example, when the rotor 1 turns (for example, in a 10 meter per second wind), the interior low pressure area 110 causes the fluid 112 to accelerate through the rotor 1 If the interior low pressure area 110 causes the rotor 1 to draw fluid 112 from an area surrounding the rotor 1 having a diameter that is 20% larger than the diameter of the rotor 1, the effective area of the rotor 1 will increase by 44%. This causes the speed of the fluid 112 through the rotor 1 to increase by 44%, and the amount of power available in the fluid 112 increases about 3 times. This increase in available power causes the angular velocity of the rotor 1 to increase, which more rapidly pushes the fluid 112 radially away from the center of the rotor 1. The interior low pressure area 110 increases in size as the fluid 112 is more strongly directed radially away from the center of the rotor 1. As the interior low pressure area 110 enlarges, the fluid 112 flowing through the rotor 1 accelerates more rapidly, increasing available power. The result is more efficient energy capture for the fluid energy converter 100 when used as a wind turbine. It should be noted that this phenomenon can also occur in other applications of the fluid energy converter 100, such as compressors, propellers, pumps, and water turbines.

Still referring to FIGS. 1 and 6, as fluid 112 is drawn from an effective area greater than the area defined by the diameter of the rotor 1, the fluid 112 adjacent to the fluid 112 approaching the front section 12 of the blades 10 is affected through viscous interaction and follows a similar path. The result is that the fluid 112 is compressed onto the outside surface of the tip 18, creating an external high pressure area 113, which surrounds the rotor 1. The internal high pressure area 111 and the external high pressure are 113 on the tips 18 increase the density of the fluid 112 that interacts with the power producing surfaces of the rotor 1, resulting in further increases in the amount of power that the fluid energy converter 100 can extract. The result is a more efficient energy capture for the fluid energy converter 100 when it is used as a wind turbine. This phenomenon can also occur in other applications of the fluid energy converter 100, such as compressors, propellers, pumps, and water turbines.

Referring now to FIG. 7, fluid dynamic properties of the rotor 1 are described. In some applications fluid 112 is directed, or moved within the rotor 1 to maximize energy extraction from the kinetic energy in the fluid 112. FIG. 7 shows a schematic section view of a blade 10 viewed from the top. Both the front section 12 and back section 22 of the blade 10 utilize a flat foil 170 in the embodiment depicted. When fluid 112 contacts the front section 12, the fluid 112 is bent into a fluid flow 127, that is, fluid 112 changes direction after it passes by the front section 12, if the front section 12 has an angle of attack relative to the flow of the fluid 112. As the front section fluid 127 moves past the front section 12, the fluid 127 changes direction and moves in a direction substantially parallel with the front section chord 11. After passing the front section 12 of the blade 10, the interior fluid 128 also rotates in a direction which is substantially opposite the direction of rotation of the rotor 1. This interior fluid 128 then contacts a back section 22 of one of the blades 10, from an angle that is different than the angle at which the fluid 112 contacts the front section 12. This results because the front section 12 has altered the direction of the flow of the interior fluid 128. Additionally, the interior fluid 128 is also moving radially out toward the tip 18. As the interior fluid 128 continues through the interior of the rotor 1 it is affected by viscous interaction with surrounding fluid 112 that has a component of its movement rotating in the same direction as the rotor 1. Thus, when the interior fluid 128 reaches the back section 22, in some embodiments the fluid 128 is not flowing in the same direction as the front section fluid 127. To create the correct of angle of attack for the interior fluid 128, the back section 22 is set at a pitch which is different in some embodiments than the front section 12 pitch. In some embodiments the pitch of the back section 22 is 10 degrees less than the pitch of the front section 12, although the pitch of the back section 22 will vary with the type of fluid 112, angular velocity of the fluid energy converter 100, purpose of the fluid energy converter 100, and velocity of the fluid 112.

Referring now to FIGS. 7 and 9, as the back section fluid 129 passes by the back section 22, its direction is again altered due to its interaction with the back section 22. The back section fluid 129 moves in a direction roughly parallel with the back section chord 22, which in some embodiments can be set at a pitch near 0 degrees. Thus, the back section fluid 129 moves in a direction that is substantially radially away from the center of the rotor 1. In FIG. 9, the direction of the back section fluid 129 is shown from behind the rotor 1 as the back section fluid 129 leaves the rotor 1. A component of the back section fluid 129 is moving radially away from the center of the rotor 1. This action further deepens the internal low pressure area 110, increases the internal high pressure area 111, and increases the external high pressure area 113, shown in FIG. 6.

Referring to FIG. 8, the effect of fluid 112 at the tip 18 is described. FIG. 8 is a schematic cross sectional front view of the profile of the tip 18. In the embodiment shown, the tip 18 has a flat foil 170 described in FIG. 5B. The rotation direction 174 is shown by the hatched curved arrow and the rotor radius 9 is shown by the hatched line. It can be seen that the tip chord 29 is not 90 degrees, or tangent, to the rotor radius 9, but has a tangential pitch which is −6 degrees, in this example. In some embodiments, as the fluid 112 is directed radially toward the tip 18 by the front section 12 and as the fluid 112 passes through the rotor 1, the fluid 112 reaches the tip 18. In some embodiments the tip 18 helps prevent the fluid 112 passing by the tip 18 from escaping the influence of the rotor 1 and minimizes tip loss. The tip 18 can alter the radial movement of the fluid 112 so that it transfers its energy to the rotor 1. A negative tangential pitch will also create tangential lift 176, the direction of which is denoted with an arrow, which has a small vector in the rotation direction 174, adding power to the rotor 1

Referring now to FIGS. 1, 3, 4 a, 4 b, 4 c, and 8, flexing of the blades 10 is described. In some embodiments, changes in the velocity of the fluid 112 and/or angular velocity of the rotor 1 can cause changes in the pitch of the front section 12, tangential pitch at the tip 18, and pitch of the back section 22 of the blades 10. In some embodiments, such as wind turbines, it is advantageous to alter these pitches with changes in the velocity of the fluid 112 and/or angular velocity of the rotor 1. In some embodiments, the blades 10 can be made to flex or bend so that these pitches decrease with an increase in the velocity of the fluid 112 and/or an increase in angular velocity. Flexing of the blades 10 can be accomplished by constructing the blades 10 of a flexible material, such as sheet metal, plastic, a composite, or other suitable material. The amount of flex in the blades 10 can be controlled by varying the thickness of the material and the length of the chord. As the velocity of the fluid 112 increases, it produces an increase in pressure on the blade 10 surface, especially at the front section 12. If the front section 12 is pushed back toward the back section 22 by the increased pressure of the fluid 112 on the front section 12 surface, the pitch of the front section 12, the tangential pitch at the tip 18, and the pitch of the back section 22 can all be configured to decrease. Typically, an increase in the velocity of the fluid 112 will cause an increase in angular velocity of the rotor 1. In many applications, increases in angular velocity will require a decrease in the pitch of the front and back sections 12, 22, and tip 18, to maintain optimum efficiency.

As the tip 18 rotates faster due to an increase in the velocity of the fluid 112, more pressure will be applied to its surface from the fluid 112, and if the blade 10 is flexible, it will be pushed tangentially back opposite the rotation direction 174 of the rotor 1. This will decrease the tangential pitch at the tip 18, which in some embodiments is desirable.

Still referring to FIGS. 1, 3, 4 a, 4 b, 4 c, and 8, in some embodiments the power train 80 is attached to the back hub 44, and the front hub 34 rotates freely. In such embodiments, the front hub 34 will rotate in advance of the back hub 44, pulling it along, due to the fact that the back hub 44 must overcome the resistance of the power train 80 torque. This rotation by the front hub 34 some number of degrees in advance of the back hub 44 typically increases when fluid 112 velocity and/or angular velocity increases. This increase in the angle of the front hub 34 relative to the back hub 44 will cause the pitches of the front and back sections 12, 22, and the tangential pitch at the tip 18, to decrease.

Referring now to FIGS. 10-14, the angle of attack of the fluid around a blade 210 will be described. The blade 210 may be similar in certain aspects to the blade 10 of FIG. 1, and may be usable with a fluid energy converter such as the fluid energy converter of FIG. 1 in a similar manner to that depicted and described above with respect to blade 10. For description purposes, axis Z refers to a coordinate axis that is perpendicular to the longitudinal axis 8 (sometimes referred to here as axis “X”, or “x-axis”). Axis Y extends out of plane of the page in FIGS. 12, 13, and 14. FIG. 11 shows the blade 210 in the X-Y plane. For illustration purposes, sections A-A, B-B, and C-C are provided in FIG. 12-14 to depict the relative shapes and relative positions of the fluid foil cross-sections of the blade 210. It should be noted that in most cases the shape of the blade 210 transitions smoothly between the sections depicted. It should also be noted that the cross-sections shown in FIGS. 12-14 are not to scale and are provided for purposes of explanation and not limitation.

Turning to FIGS. 12-14, a front root fluid foil 310 and a back root fluid foil 312 are shown in the X-Z plane. Fluid 320 flow direction is depicted schematically by arrows. In some embodiments, the front root fluid foil 310 is thicker than a front tip fluid foil 330 (FIG. 14) to increase structural strength of the blades 210. The angular velocity near the longitudinal axis 8 can be lower than the angular velocity near a tip 218. Therefore it can be advantageous to have the front root fluid foil 310 thicker than the front tip fluid foil 330. In some embodiments, the front root fluid foil 310 is configured to have a zero degree angle of attack and a pitch 311 of 57 degrees between the Z axis and the front root chord 314. In other embodiments, the angle of attack of the fluid 320 can vary between 12 and −12 degrees depending on the angular velocity of the blades 210 and the velocity of the fluid 320. In yet other embodiments, the pitch 311 of the front root fluid foil 310 can vary greatly, from 1 degree in high angular velocity applications such as compressors, to 89 degrees in applications where the fluid energy converter 100 is spinning slowly and the fluid 320 has a high velocity.

In some embodiments, the back root fluid foil 312 can be thinner than the front root fluid foil 310. In some embodiments, such as wind turbines, the back root fluid foil 312 will have a higher angle of attack than the front root fluid foil 310 to facilitate the extraction of kinetic energy from the fluid 320. In some embodiments, the back root fluid foil 312 is configured to have a ten degree angle of attack and a pitch 313 of 44 degrees between the Z axis and the back root chord 316. In other embodiments, the angle of attack of the fluid 320 can vary between 22 and −4 degrees depending on the angular velocity of the blades 210 and the velocity of the fluid 320. In other embodiments, the pitch 313 of the back root fluid foil 312 can vary greatly, from 1 degree in high angular velocity applications such as compressors, to 89 degrees in applications where the fluid energy converter 100 is spinning slowly and the fluid 320 has a high velocity.

Referring now to FIG. 13, in one embodiment, the angle of attack at the front fluid foil 322 is higher than the front root fluid foil 310. In some embodiments, the front fluid foil 322 is configured to have a five degree angle of attack and a pitch 323 of 20 degrees between the Z axis and the front chord 324. In other embodiments, the angle of attack of the fluid 320 can vary between 12 and —4 degrees depending on the angular velocity of the blades 210 and the velocity of the fluid 320. In yet other embodiments, the pitch 323 of the front fluid foil 322 can vary greatly, from 1 degree in high angular velocity applications such as compressors, to 89 degrees in applications where the fluid energy converter 100 is spinning slowly and the fluid 320 has a high velocity.

In one embodiment, the angle of attack at a back fluid foil 325 is higher than the front fluid foil 322. In some embodiments, the back fluid foil 325 is configured to have an eight degree angle of attack and a pitch 326 of 19 degrees between the Z axis and the back chord 327. In other embodiments the angle of attack of the fluid 320 can vary between 22 and −2 degrees depending on the angular velocity of the blades 210 and the velocity of the fluid 320. In yet other embodiments, the pitch 326 of the back fluid foil 325 can vary greatly, from 1 degree in high angular velocity applications such as compressors, to 89 degrees in applications where the fluid energy converter 100 is spinning slowly and the fluid 320 has a high velocity.

Referring now to FIG. 14, in one embodiment, the angle of attack at the front tip fluid foil 330 is higher than the front root fluid foil 310. In some embodiments, the front tip fluid foil 330 is configured to have a five degree angle of attack and a pitch 331 of 20 degrees between the Z axis and the front tip chord 318. In other embodiments, the angle of attack of the fluid 320 can vary between 18 and −4 degrees depending on the angular velocity of the blades 210 and the velocity of the fluid 320. In yet other embodiments, the pitch 331 of the front tip fluid foil 330 can vary greatly, from 1 degree in high angular velocity applications such as compressors, to 89 degrees in applications where the fluid energy converter 100 is spinning slowly and the fluid 320 has a high velocity.

In one embodiment, the angle of attack at a back tip fluid foil 332 is higher than the front tip fluid foil 330. In some embodiments, the back tip fluid foil 332 is configured to have an eight degree angle of attack and a pitch 333 of 19 degrees between the Z axis and the back tip chord 319. In other embodiments the angle of attack of the fluid 320 can vary between 20 and −2 degrees depending on the angular velocity of the blades 210 and the velocity of the fluid 320. In yet other embodiments, the pitch 333 of the back tip fluid foil 332 can vary greatly, from 1 degree in high angular velocity applications such as compressors, to 89 degrees in applications where the fluid energy converter 100 is spinning slowly and the fluid 320 has a high velocity.

While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others.

It should be noted that the description above has provided dimensions for certain components. The mentioned dimensions, or ranges of dimensions, are provided in order to comply as best as possible with certain legal requirements, such as best mode. However, the scope of the inventions described herein are to be determined solely by the language of the claims, and consequently, none of the mentioned dimensions is to be considered limiting on the inventive embodiments, except in so far as anyone claim makes a specified dimension, or range of thereof, a feature of the claim.

The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention can be practiced in many ways. As is also stated above, it should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the invention with which that terminology is associated. 

1. A rotor for a fluid energy converter, the rotor comprising: a longitudinal axis; a front rotatable hub coaxial with the longitudinal axis; a back rotatable hub coaxial with the longitudinal axis; a plurality of blades, each blade comprising a front section, a tip, and a back section; wherein the blades are arranged angularly about the longitudinal axis; wherein each blade is attached at a front root attachment to the front hub and attached at a back root attachment end to the back hub; and wherein the front section comprises a pitch higher than a pitch of the back section.
 2. The rotor of claim 1, wherein the rotor produces a high pressure area at an exterior surface of the blade tips.
 3. The rotor of claim 1, wherein the low pressure area begins near the front section of the blades, and wherein the difference between the low pressure area and a surrounding pressure increases toward the back section of the blades.
 4. The rotor of claim 1, wherein pressure increases within the rotor as the distance from the longitudinal axis increases.
 5. The rotor of claim 1, wherein the front section causes the fluid to be deflected radially away from the longitudinal axis.
 6. A rotor for a fluid energy converter, the rotor comprising: a longitudinal axis; a front rotatable hub coaxial with the longitudinal axis; a back rotatable hub coaxial with the longitudinal axis; at least nine blades, each blade attached at a front section to the front hub and attached at a back section to the back hub, the blades positioned radially around the longitudinal axis, wherein each of at least some of the blades comprises a front section, a tip, and a back section; wherein the front section, tip, and back section use fluid foils; and wherein the tip chord angle is between 4 and −15 degrees.
 7. A fluid energy converter, comprising: a longitudinal axis; and a rotatable rotor coaxial about the longitudinal axis, wherein the rotatable rotor includes a plurality of blades, each blade comprises of a front section, a tip, and a back section; and wherein the tip chord produces tangential lift.
 8. The fluid energy converter of claim 7, which is a wind turbine with at least nine blades and where fluid accelerates through the rotor.
 9. The fluid energy converter of claim 7, further comprising a front curve, and where the front curve transitions from a primarily axial direction along the longitudinal axis to a primarily radial direction perpendicular to the longitudinal axis.
 10. The fluid energy converter of claim 9, where the front curve is designed to deflect fluid radially away from the longitudinal axis.
 11. A rotor for a fluid energy converter, the rotor comprising: a longitudinal axis; a front rotatable hub coaxial with the longitudinal axis; a back rotatable hub coaxial with the longitudinal axis; a plurality of blades, each blade comprising a front section, a tip, and a back section; wherein the blades are arranged angularly about the longitudinal axis; wherein each blade is attached at a front root attachment to the front hub and attached at a back root attachment end to the back hub; and wherein the front section near the front rotatable hub has an angle of attack that is lower than the angle of attack at back section near the back rotatable hub.
 12. The fluid energy converter of claim 11, where the difference between the angle of attack of the front section and the back section is greater near the front and back rotatable hubs than at the tip. 